Thermosensitive laminated metals



Nov. 20, 1956 2,770,870

V. G. MOORADIAN THERMOSENSITIVE LAMINATED METALS Filed May 51, 1952 ATTO RN EYS United States Patent O TI-IERMOSENSITIVE LAMINATED METALS Victor G. Mooradian, East Orange, N. J., assignor to The H. A. Wilson Company, Newark, N. J., a corporation of New Jersey Application May s1, 1952, serial N0. 290,963 7C1aims. (cl. 29-19s.s)

Vof S51/2% to 61% cobalt, 8% to,101/2% chromium, and

301/2 to 351/2 iron in combination With a companion component of metal of relatively high coecient of thermal expansion.

Thermosensitive laminated metals lsuch as bimetal thermostat coils, and other thermosensitive articles, often must be subjected to corrosive conditions when in use.

For example, thermostatic valves in water circulation systems commonly employ bimetal thermostat elements -which are immersed in the circulating water and therein are subjected to decidedly corrosive conditions. A common type of thermostatic bimetal comprises a high ex- .panding layer of brass or of a steel alloy securely bonded to a low expanding layer of Invar (36% to 45% nickel, balance iron) and such bimetals are quite unsatisfactory for use under corrosive conditions both because the steel and Invar components oxidize readily land even the brass may corrode chemically, and because a corrosive electromotive couple between the two components of the bimetal may be formed 1n an aqueous liquid. For use under corrosive conditions, therefore,

lmuch elort has been devoted to the design of thermosensitive bimetals whichare resistant vboth 4to simple chemical and to electrochemical corrosion. The problem has not been an easy one, for modifications in the composition of the Invar or other low expanding component which enhance its corrosion resistance are generally 4found also to increase its coefficient of thermal expansion. Similarly, it is extremely diicult to devise alloys which are more corrosion resistant than the common brasses and which at the same time possess higher coeilicients of thermal expansion. As a result the bimetals heretofore produced which are most satisfactory from the standpoint of possessing a high degree of corrosion resistance are delicient with respect to their deflection properties when subjected to a change in temperature, i. e, the flexivities (the change in curvature of the bimetal strip per unit temperature change per unit thickness) of the most corrosion-resistant thermosensi- -tive bimetals heretofore known are very considerably lower than the ilexivities of the conventional brass-Invar or steel alloy-Invar bimetals.

' The present invention yprovides an improved thermosensitive article in which an operating component of relatively low coefficient of thermal expansion consisting essentially of S51/2% to 61% cobalt, 8% to lOl/2% chromimurn, and SOI/2% to 351/2% iron is connected in thermally responsive association with a companion opgerating component made of metal of relatively high coecient lof thermal expansion. In the particular case .fully and fully annealed metal.

Patented Nov. 20, 19.56

of thermosensitive laminated metals, a layer of a metal of the aforesaid composition forms the low expanding component and is joined to a layer of metal having a relatively high coeicient of thermal expansion. This low expanding component is remarkably resistant to `corrosion. Moreover, its coeicient of expansion is low enough so that when it is used to make thermosensitive bimetal in combination with the most corrosion-resistant cupreous alloys (such as the silicon-copperalloys containing 0.5% to 5% silicon and the balance essentially all copper), the liexivity of the resulting bimetal is substantially higher than that of any bimetal heretofore known possessing good corrosion resistance.

As a preferred embodiment of the invention, the new thermosensitive laminated metal is described below with particular reference to the accompanying drawing, the single figure of which is a ternary diagram of a portion of the cobalt-chromium-iron system, showing the region thereof kthat is employed in the manufacture of low expanding components of thermosensitive laminated metals Vmade in accordance with the invention.

The fact that? certain alloys of cobalt, iron, and chromivum possess extremely small coeflicients of thermal :ex-

v Reports, Thku Imp. Univ., vol. 23 (1934) pages 265- 280). Notwithstanding these desirable properties, the

yalloys investigated by Masumoto never came into use as low expanding components of the thermoresponsive laminatedmetal, evidently for two reasons. First, the lowest coefficients of thermal expansion that are found in the cobalt-chromium-iron system occur only in care- When the alloys with such low expansion coellicients are cold-worked even to a slight extent, the expansion coeicient is increased to a very large extent, often by a factor of three or four. Since thermosensitive metals generally are made and used in the cold-rolled condition, this characteristic of the minimum-expansion Masumoto alloys has greatly reduced their attractiveness as components of such products. Second, the coefficient of thermal expansion of the Masumoto alloys in the area where this coeicient is minimum is extremely sensitive to very small changes in composition of the alloy. A change as small as 1A percent in the amount of chromium or cobalt present in the alloy, for example, may bring about a several-fold change in the coefficient of expansion of the alloy. It is not possible as a practical matter to hold the composition of commercially made alloys within the extremely narrow ranges required to secure reliable reproduction of the minimum coefficient of thermal expansion of the Masumoto alloys.

In the course of an exhaustive investigation of cobaltchromium-iron alloys, l have discovered that there is a composition region removed from that of minimum coefficient of thermal expansion, where such coetlicient is low enough to be of substantial value for use in the manufacture of thermosensitive laminated metals withoutalloy composition which I have found to be especially suitable for use in the manufacture of thermosensitive laminated metal is that embraced within the line X-X-X. It is a region of smaller iron concentration andl higher cobalt concentration than that in which annealed alloys exhibit minimum coefficients of thermal expansion (the latter are to be found in the area within the lineiZZ-Z of the accompanying drawing). It is, however, a region within which the coefficient of thermal expansion is not markedly increased byr cold-working the alloy; indeed, it is a region wherein such` coefficient is in general even less for the cold-worked metal than is the case in the area Z-Z-Z where the coefficient is minimum for fully annealed metal. Moreover, it is a region of broad enough extent so that the composition of alloys made commercially can be kept well within it, and in which such variations in alloy compositions as do occur commercially do not significantly affect the coeicient of thermal expansion of either the cold-worked or the annealed metal.

The foregoing is evident from a consideration of the numerical data appearing on the accompanying drawing. The figures connected by lead lines to dots within the borders of the diagram indicate the coefficients of thermal expansion of the alloys having the composition denoted by such dots. Figures preceded by the letter A, when multiplied by l6, give the coefficients of thermal expansion of the indicated alloys in the annealed condition, and figures preceded by the letters CW, when multiplied by give the coeicients of thermal expansion of the indicated alloys in the cold-worked condition resulting from cold-rolling 50% reduction in area.

It will be noted that in general alloys lying within the region bounded by the line Xa-X-X have rather small coeliicients of thermal expansion in the coldaworked condition (mostly less than 4,5Xl0-6), and also that such coefficient is not much different for the cold-worked metal than it is for the annealed metal. In these respects the alloys within the region X-X-X differ substantially from the alloys within the area Z-Z-Z. In this latter area the coefiicient of thermal expansion of the alloy in the annealed condition is extremely low (generally less than ZXlO-G, and Masumoto has even reported some alloys within this region having a negative coetcient); but the expansion coecient of the same alloys in the coldworked condition is very much higher than for the annealed metal, and, indeed, is even higher in many instances than for similarly cold-worked metal within the region X-XX. Further, it will be noted that within the area Z'-ZZ the coefficient of thermal expansion, particularly of the annealed metal, is extremely sensitive to composition changes, especially to changes in chromium concentration, whereas no such sensitivity is apparent for the alloys lying within the region X-X--X-` In the latter region, variations up to about 1i% in the amount of any of the ingredients of the alloy do not significantly affect such coefficient. Accordingly, while annealed alloys within the area Z-Zf-Z possess the smallest coefficients of thermal expansion which it is possible to achieve in alloys of the cobalt-chromium-iron series, such alloys are not suitable for commercial use in the manufacture of thermosensitive laminated metals, whereas I have found that alloys lying within the region X-X-X are eminently suited for such purpose.

Within the region X-X-X I nd that alloys containing from 56% to 59% cobalt, from 8% to 10% chromium, and from 32% to 35% iron are especially suitable for use in the manufacture of thermoresponsive laminated metals. This composition range includes the area Y-Y--Y on the accompanying drawing, within which the coeicient of thermal expansion of cold-worked metal is generally less than 3.5 l0-6 and is particularly insensitive to the degree of cold work and to minor variations in composition. Accordingly the area Y-Y-Y is that within which it is usually most advantageous to maint-ain the composition of alloys for use as the low expanding component of thermostatic bimetals. Indeed, the region Y-Y-Y may be considered as the region within which normal commercial variations from a nominal composition of 57% cobalt, 9% chromium, and 34% iron will occur; and it is this nominal composition that I have found to be of most general utility `in the manufacture of corrosion-resistant thermoresponsive bimetals.

In` the manufacture of corrosion-resistant thermoresponsive bimetals in accordance with the invention, a bar of cobalt-chromium-iron alloy of the character described above, containing from S51/2% to 61% cobalt, from 8% to lOl/2% chromium, and from 301/z% to 351/2 iron, is bonded to a bar of a metal of relatively higher coefficient of thermal expansion. Preferably the latter is a bar of a cupreous alloy, especially a copper-silicon alloy containing 0.5% to 5% silicon, and the balance essentially all copper. The manner in which the two bars are bonded together is conventional, e. g. by brazing or by silver soldering. The resulting composite bar is then rolled down in the usual manner to form a bimetallic sheet or strip of the desired final thickness. In conformity with usual practice in the manufacture of `composite metals, the sheet or strip is cold nished with a cold-rolling operation that entails at least reduction in area and most commonly to 50% reduction in area, so that in the finished composite metal the grain Structure of each layer thereof isy elongated to the exent characteristic of such cold-working.

Cobalt-chromium-iron alloys of the composition contemplated by this invention are substantially as resistant to ordinary chemical and electrochemical types of corrosion as are the well-known stainless steels. Consequently bimetals in which a component of this alloy is used in combination with a good corrosion-resistant cupreous alloy of relatively high coeicient of thermal expansion is excellently suited for use in environments which are too corrosive for ordinary thermosensitive bimetals. For example, bimetals according to the invention may be directly immersed in circulating aqueous media in which ordinary brass-Invar or steel-Invar bimetals would be quickly corroded to the point of becoming inoperative, and even under such conditions the new bimetal will perform properly over a long service life.

As previously noted, the coeicient of thermal expansion of cobalt-chromium-iron alloys of compositions within the range contemplated by the invention are approximately the same for the metal in the cold-worked state as for the metal in the annealed state. Consequently thermoresponsive composite metals having deflection characteristics that are maintained uniform within commercial tolerances may be produced in the cold-worked state without the need for more than normal care in controlling the character and extent of the annealing and cold-working operations to which the metal is subjected during manufacture. Also, because of the relative insensitivity of the coetiicient of thermal expansion of these cobalt-chromium-iron alloys to changes in composition, it is easily possible to produce composite metals according to the invention in which the deflection characteristics are consistently maintained within commercial tolerances without exercising more than normal commercial care in controlling the composition of the alloy which forms the low expanding component.

Bimetals according to the invention in which a cobaltchromiumiron component is employed in combination with a silicon-copper component (containing nominally 1.5% silicon, balance copper) possessexivities normally within the range from 90x10-F1 to 1O0 l07. While this is low compared with the flexivity of a good brass- Invar or steel-Invar bimetal (for which the llexivity will generally be about l 10-7; or even higher)7 it is very much superior to what can be obtained with the bestV truly corrosion-resistant bimetals heretofore produced commercially (for which the fiexivity often does not exceed 10-7).

While particular reference has been made herein to bimetals having a high-expansion component of siliconcopper alloy, it is of course understood that other corrosion-resistant materials, both cupreous and copper-free, may be used in its place. For example, among cupreous metals a naval brass or an aluminum bronze, or a cupronickel alloy, may in some cases be advantageously used as the high expanding component; or a non-cupreous metal such as a stainless steel may if desired be used for such purpose.

Also, while particular reference has been made herein to thermosensiitve laminated metals, it is to be remembered that there are thermosensitive articles or devices in which the low expanding component is not a component of a bmetal but is simply a mechanical component or element of the device, and Works in thermally responsive association with a physically separate companion component or element made of a metal of relatively high coeicient of thermal expansion. The invention encompasses such articles or devices as fully as it encompasses the common thermosensitive bimetals.

I claim:

1. Thermosensitive laminated metal in which a layer of metal of relatively low coeicient of thermal expansion consisting essentially of S51/2% to 61% cobalt, 8% to lOl/2% chromium, and 301/2% to S51/2% is bonded to a layer of metal of relatively high coeicient of thermal expansion, the coecient of thermal expansion of said low expanding layer being substantially unaffected by small variations in the degree of cold working and by variations up to about Mt in the amount of any of the above specied ingredients.

2. Thermosensitive laminated metal according to claim 1 in which the layer of metal of relatively low coecient of thermal expansion consists essentially of 56% to 59% cobalt, 8% to 10% chromium, and 32% to 35% iron.

3. Corrosion-resistant thermosensitive bimetal in which a layer of metal of relatively low coeicient of thermal expansion consisting essentially of S51/2% to 61% cobalt, 8% to lOl/2% chromium, and B01/2% to 351/2% iron is bonded directly to a layer of metal of relatively high coecient of thermal expansion consisting of 0.5% to 5% silicon and the balance esentially all copper, the coefficient of thermal expansion of said low expanding layer being substantially unaffected by small variations in the degree of cold Working and by variations up to about M: in the amount of any of the stated ingredients thereof.

4. Corrosion-resistant thermosensitive bimetal according to claim 3, in which the layer of metal of relatively low coeicient of thermal expansion consists essentially of about 57% cobalt, about 9% chromium, and about 34% iron.

5. Thermosensitive laminated metal in which a layer of metal of relatively low coeicient of thermal expansion consisting essentially of S51/2% to 61% cobalt, 8% to 10i/2% chromium, and 301/z% to 35i/2 iron is bonded to a layer of metal of relatively high coefcient of thermal expansion, the grain structure of each of said layers of metal being elongated at least to the extent characteristic of 25% reduction in area at room temperature, and the coefficient of expansion of said low expanding layer being less than 4.5 10*6 and being substantially unaffected by small variations in the degree of cold working of said layer and by variations up to about in the amount of any of the above-stated ingredients thereof.

6. Corrosion-resistant thermosensitive bimetal in which a layer of metal of relatively low coelcient of thermal expansion consisting esentially of about 57% cobalt, about 9% chromium, and about 34% iron is bonded directly to a layer of metal of relatively high coefficient of thermal expansion consisting essentially of 0.5% to 5% silicon and the balance copper, the grain structure of each of said layers of metal being elongated at least to the extent characteristic of 25% reduction in area at room temperature, and the coeicient of expansion of said low expanding layer being less than 4.5 X10B and being substantially unaffected by small variations in the degree of cold Working of said layer and by variations up to about in the amount of any of the above-stated ingredients thereof.

7. A thermosensitive article of the character described in which an operating component of relatively low coeicient of thermal expansion consisting essentially of 55Vz% to 61% cobalt, 8% to lOl/2% chromium, and 3D3/2% to 351/z% iron is connected in thermally responsive association with a companion opearting component made of metal of relatively high coecient of thermal expansion, the coeicient of expansion of said low expanding component being substantially unaffected by small variations in the degree of cold working thereof and by variations up to about 1A% in the amount of any of its above-stated ingredients.

References Cited in the le of this patent UNITED STATES PATENTS 1,190,652 Henderson July 11, 1916 1,522,813 Etchells Jan. 13, 1925 1,643,809 Fry Sept. 27, 1927 1,652,546 Vaughan Dec. 13, 1927 1,671,491 Scott May 29, 1928 1,689,814 Brace Oct. 30, 1928 1,929,655 Scott Oct. 10, 1933 1,948,121 Matthews Feb. 20, 1934 1,987,714 Scott Ian. 15, 1935 2,075,014 Bassett Mar. 30, 1937 2,366,178 Chace Jan. 2, 1945 2,482,900 Chace Sept. 27, 1949 2,513,303 Feild July 4, 1950 FOREIGN PATENTS 405,607 Great Britain Feb. 2, 1934 

1. THERMOSENSITIVE LAMINATED METAL IN WHICH A LAYER OF METAL OF RELATIVELY LOW COEFFICIENT OF THERMAL EXPANSION CONSISTING ESSENTIALLY OF 551/2% TO 61% COBALT, 8% TO 131/2% CHROMIUM, AND 301/2% TO 351/2% IS BONDED TO A LAYER OF METAL OF RELATIVELY HIGH COEFFICIENT OF THERMAL EXPANSION, THE COEFFICIENT OF THERMAL EXPANSION OF SAID LOW EXPANDING LAYER BEING SUBSTANTIALLY UNAFFECTED BY SMALL 